Artist: Anthony Van Dyck (1599-1641) painted, to borrow Satan's description of his court of downcast angels in Paradise Lost, "Princes, Potentates,/ Warriors, the Flow'r of Heaven". Van Dyck was court painter to Charles I, by far the most visually literate British monarch. He was central to Charles's attempt to give his monarchy the opulence and glory of European baroque courts - a disastrous policy. The very European and Catholic flavour of the art produced for Charles - who employed some of the continent's leading artists, including Rubens and Orazio Gentileschi, assisted by his daughter Artemisia - only fuelled the hatred of the Puritans, to whom fancy court art looked like papist idolatry and monarchical arrogance. Van Dyck, who trained in Antwerp and developed his own, more pragmatic version of Rubens's style, was the European artist who best fitted the Stuart court.

While you could never mistake Rubens for a Brit, there was an empiricism about Van Dyck, a commitment to the portrait as documentary and not just vastly flattering art, that had an instantly local quality. Van Dyck's portraiture makes him a founder of British art - and his vision of the nobility on the eve of the civil war helped to enshrine in the national memory a sentimental image of cavalier royalism.

Subjects: Lord John and Lord Bernard Stuart, sons of the third Duke of Lennox, were killed fighting in the civil war in 1644 and 1645 respectively. They had participated in the European culture promoted by Charles I, posing for this painting just before a proposed Grand Tour. They were in their 20s when they died - and in their teens in this painting.

Distinguishing features: If style alone could have won the English civil war, surely the parliamentary cause would have been hopeless. These two young men so perfectly fit the mythic image of romantic, long-haired, swaggering cavaliers that the painting could be a Victorian historical scene in the manner of And When Did You Last See Your Father?

And yet it is a portrait done before the war (about 1638), when Lord John and Lord Bernard had long, rich, powerful lives ahead of them. And don't they know it? Were they actually trying to provoke the populace? Lord Bernard, on the right, looks at us in snotty disdain. He couldn't be prouder of the way he looks in his blue and silver silk suit, his sword at his side, his gloves dangling from his hand on his hip, as if he had just slapped someone and demanded satisfaction. Lord John is a quieter, more self-involved figure, although posed on stone steps to make him look impressive.

These variations are harmonised in a brilliant formal arrangement, as if they were exotic flowers arranged in a vase for maximum chromatic effect. Lord John's gold and bronze complements the harder silver and blue garb of Lord Bernard, just as one's smooth, long hair sets off the other's curls. They have the same long, distinctive face, although one brother has a better chin. Strange how the same pedigree can be ugly in one, handsome in the other. And yet for all the differences, they are two of a kind.

Inspirations and influences: Gainsborough made a copy of this painting, and Sir Joshua Reynolds was also influenced by Van Dyck's hyperbole. In reaction against this kind of glamour portrait, Oliver Cromwell insisted, when he posed for an official image, that it be plain and accurate, warts and all.